Dear all

I was trying to calculate the thermal conductivity of Si nanowire with Radius 75A at T=300K but I am getting very small value, 0.027[W/mK]. It should some how be around 100 [W/mK].

units real

variable T equal 300

variable V equal vol

variable dt equal 4.0

variable p equal 200 # correlation length

variable s equal 5 # sample interval

variable d equal $p*$s # dump interval

# convert from LAMMPS real units to SI

variable kB equal 1.3806504e-23 # [J/K] Boltzmann

variable kCal2J equal 4186.0/6.02214e23

variable A2m equal 1.0e-10

variable fs2s equal 1.0e-15

variable convert equal {kCal2J}*{kCal2J}/{fs2s}/{A2m}

# setup problem

dimension 3

boundary p p p

atom_style atomic

lattice diamond 5.43

region whole block 0 200 0 200 0 100 units box

create_box 1 whole

region wire cylinder z 100 100 75 INF INF units box

lattice hcp 5.43 orient x 1 0 0 orient y 0 1 0 orient z 0 0 1

create_atoms 1 region wire

mass 1 28.8

pair_style tersoff

pair_coeff * * …/potentials/Si.tersoff Si

timestep ${dt}

thermo $d

# equilibration and thermalization

velocity all create $T 102486 mom yes rot yes dist gaussian

fix NVT all nvt temp $T $T 10 drag 0.2

dump 1 all custom 1000 Sigeometry.* id type x y z

run 10000

shell mkdir Silicon

shell cd Silicon

# thermal conductivity calculation

unfix NVT

fix NVE all nve

reset_timestep 0

compute myKE all ke/atom

compute myPE all pe/atom

compute myStress all stress/atom virial

compute flux all heat/flux myKE myPE myStress

variable Jx equal c_flux[1]/vol

variable Jy equal c_flux[2]/vol

variable Jz equal c_flux[3]/vol

fix FLX all ave/correlate $s $p $d &

c_flux[1] c_flux[2] c_flux[3] type auto file Silicon.dat ave running

variable scale equal {convert}/{kB}/$T/$T/$V*s*{dt}

variable k11 equal trap(f_FLX[3])*{scale}
variable k22 equal trap(f_FLX[4])*{scale}
variable k33 equal trap(f_FLX[5])*${scale}

thermo_style custom step temp v_Jx v_Jy v_Jz v_k11 v_k22 v_k33

run 10000

variable k equal (v_k11+v_k22+v_k33)/3.0

print "average conductivity: $k[W/mK] @ $T K "

Thaks